Companies are currently in the process of increasing the size and complexity of their storage systems to keep pace with increasing data. For this reason, the companies are seeking to facilitate the management and enhance the utilization efficiency of storage apparatuses.
One technology for meeting these demands is thin provisioning. In thin provisioning, the storage system provides a host computer with a virtual logical volume (hereinafter, a virtual volume) that does not comprise a physical storage area. The storage system dynamically allocates a page inside a pool to the virtual volume in accordance with a write request to the virtual volume from the host computer. A “pool” is a cluster of pool volumes. A pool volume comprises multiple pages. A “page” is a physical storage area.
According to thin provisioning technology, it is possible to efficiently use the capacity of the storage system, and, in addition, to easily perform a storage system capacity design. This is because in thin provisioning, a page may be allocated in accordance with the actual usage of the virtual volume.
A pool is generally comprised of media (a group of pages) of the same performance. However, the access frequencies of multiple pages allocated to a virtual volume are normally not the same. Among the multiple pages allocated to the virtual volume are a mix of high access frequency pages and low access frequency pages. Therefore, in a technology that allocates pages of the same performance to the virtual volume, performance excesses and deficiencies may occur.
For example, in a case where a pool comprises only high-performance media (high-performance pages), a performance overload will occur with respect to a low access frequency page. Alternatively, in a case where a pool comprises only low-performance media (low-performance pages), a performance deficit will occur with respect to a high access frequency page.
One method for solving this problem is disclosed in Patent Literature 1. According to Patent Literature 1, one pool is hierarchized by comprising multiple media of different performance. The data in a page is reallocated from the tier, which comprises this page, to a tier that is optimal for the access frequency of this page.
Furthermore, technology for incorporating a logical volume of another storage apparatus inside its own apparatus, and providing this logical volume to the host computer as if it were its own logical volume is known (Patent Literatures 2 and 3).